1. Technical Field
The present invention relates to a scanning image display system and a scanning image display.
2. Related Art
In recent years, scanning image displays have been adapted so as to display an image by raster-scanning a light beam such as a laser beam on a projection surface.
In order to generate an image using the scanning image display, it is necessary to scan a light beam two-dimensionally using a scanner such as a polygon mirror or a galvanometer mirror. Although a two-dimensional method of scanning a light beam can be used where a single scanner scans in both the horizontal and vertical directions, the resulting scanner is more complicated and difficult to control. Therefore, scanning image displays are typically provided with two sets of scanners, each of which scans along one dimension using a single light beam. Thus one light beam scans in the horizontal direction and one scans in the vertical direction. In the past, it has been common to use polygon mirrors or galvanometer mirrors in each of the scanners, and a projection device using rotating polygon mirrors for both of the scanners has been proposed (see e.g., Japanese Patent Application No. JP-A-1-245780).
Further, in recent years, there is proposed a technology which uses a plurality of projectors to form a large screen by projecting a plurality of projection images respectively projected from a plurality of projectors onto a screen in a tiling manner, (see Japanese Patent Application Nos. JP-A-1-228281 and JP-A-3-75685). As described above, there has been proposed a method of projecting the same display images on a screen in an overlapping manner, thereby achieving higher luminance of the image, correcting a luminance variation of the image, and enhancing color expression (enlarging the color reproduction area), thus increasing the number of gray-scales and the resolution.
The multi-projection television described in the JP-A-1-228281 combines projection televisions with the same structure by coupling the televisions together in the vertical and horizontal directions via a coupling member. Thus, since the projection televisions located in an upper part with the coupling member can be moved in an anteroposterior direction, the seam between the front surfaces of the screen can be reduced to the minimum.
The projecting image display described in the JP-A-3-75685 is provided with a plurality of projectors, which display divisional images by dividing the image to be projected on the liquid crystal panels of the projectors, respectively, and enlarging and projecting the divisional images on a screen, so that the images are displayed adjacent to each other, thereby displaying the entire image. In this case, the liquid crystal pixels and the screen pixels on the screen correspond one-to-one, and that the intervals of the screen pixels are equal. Therefore, since the positions of the liquid crystal pixels for displaying the image are always fixed on the screen, it becomes possible to obtain a large-sized image in which the boundaries between the adjacent images of the respective projectors are not visible.
However, although a polygon mirror, a galvanometer mirror, an MEMS mirror (a resonant mirror) an acousto-optic (AO) element, an electro-optic (EO) element, and as the like may be used as the scanner scanning the image display, an MEMS mirror is preferable as the scanner for satisfying the both requirements of a large-sized screen (a large deflection angle of the scanner) and high resolution (high-speed driving, and a large area of the mirror).
However, one difficultly with using the MEMS mirror, however, is that the MEMS mirror utilizes resonance of the system in order for obtaining a large deflection angle, meaning that if the drive frequency of the MEMS mirror is shifted from the resonant frequency, it is difficult to achieve a large deflection angle as desired. Since the resonant frequency of the MEMS mirror varies depending on absorption of the heat of the laser beam and the ambient temperature, in the case of scanning the MEMS mirror at a high speed, it is necessary to vary the drive frequency to correspond with variations in the resonant frequency.
However, if the heat is accumulated in the MEMS mirror, the resonant frequency of the MEMS mirror is lowered, and if the drive frequency of the MEMS mirror is set lower than a certain level, there is insufficient time to draw one frame and the frame is dropped.
Further, in the scanning image display system adapted to use a plurality of scanning image displays using the MEMS mirrors to perform display by arranging the images formed by the respective scanning image displays, since the plurality of MEMS mirrors operate at respective resonant frequencies, it is difficult to synchronize all the MEMS mirrors of the respective scanning image displays. This is caused by the characteristic that the heat accumulation of the MEMS mirror causes the resonant frequency thereof to be lower as described above. Therefore, when a substantial amount of heat is accumulated in the MEMS mirror, dropped frames may result, causing a flicker in the resulting image.